Right now i have a 2.25 b-pipe. I just picked up a dc jdm header and 2.5 testpipe. Do i need a 2.5 b-pipe or am I ok with the 2.25 currently on my car? Will the bottleneck hurt my HP alot? Will i have any trouble bolting on the 2.5 testpipe with my 2.25 b-pipe?

 

thats exactly what im running. more backpressure for the streets

 

So did it bolt up too or did you have to take it to a muffler shop? Isn't back pressure worse? Thanks for the reply.

 

thats axactly what you want, more backpressure for the streets. im gonna put a 1.5" reducer on my muffler to restrict flow even more for more backpressure.

the correct wat to do it is if you have any changes in diameter it should go from smaller to larger. chances are your b pipe wont fit (think about it 2.5" to 2.25") but they do make adapters or you could just have a 2.5" flange welded on yout current b pipe. for maximum performance though look into a true 2.5" cat back.

heres a good place to go for that
http://www.accordinglydone.com...aa3a9

 

Ideally, you'd have an exhaust system that tapers down as you get further away from the heads exhaust ports.

Exhaust gas temperature is based on the velocity of the gas molecules. As you get further away from the exhaust ports, the exhaust gasses will lose heat (cool down) and as a result, slow down.

As you know, increasing an exhaust pipe's diameter will reduce the travel velocity of gases going through it. Use too big a pipe, and the exhaust velocity gets too slow. The opposite is true also. You can taper down the exhaust pipe diameter to increase the velocity of gases coming out.

What you're doing is:

Header Collector ->> Catalytic Converter / Test Pipe ->> Exhaust B-Pipe

(2.5") ->> (2.5") ->> (2.25")

This should work pretty well, though the exhaust gas temperature will likely not change much from the header to b-pipe transition. Proponents of straight through, single diameter systems, would call that a bottleneck. If you had something in place of the testpipe that would reduce exhaust gas temperature enough, then the narrowing of exhaust pipe diameter would probably help (ie: catalytic converter).

In conclusion, get a 2.5"->2.25" high flow cat instead of a test-pipe, and it'll work better

And contrary to popular myth, backpressure is not good for these motors. Backpressure is the inhibition of flow and means that the engine has to overcome those restrictive forces in addition to pushing exhaust gasses out. The 'exhaust scavenging effect' you may have heard of is an example of negative backpressure, where gasses exiting the exhaust pull along following gasses behind it.

I suppose the reason why tapered exhaust systems are not common is because it is expensive to create piping with smooth cone shaped transitions, and probably do not produce significant benefits in vehicles lacking temperature-changing elements (ie: catalytic converters) in the exhaust system.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JCushing &raquo;</TD></TR><TR><TD CLASS="quote">thats axactly what you want, more backpressure for the streets. im gonna put a 1.5" reducer on my muffler to restrict flow even more for more backpressure.

the correct wat to do it is if you have any changes in diameter it should go from smaller to larger. chances are your b pipe wont fit (think about it 2.5" to 2.25") but they do make adapters or you could just have a 2.5" flange welded on yout current b pipe. for maximum performance though look into a true 2.5" cat back.

heres a good place to go for that
http://www.accordinglydone.com...aa3a9 </TD></TR></TABLE>
wow, never knew that. Yeah, i think going from 2.5 to 2.25 is the exact opposite from what your talking about. Then i have to take a trip to the muffler shop. Thanks for the site too

 

luckily i didnt have to go to the muffler shop at all. im running the dc jdm 4-1, 2.5 inch test pipe, and dc sports cat back exhaust. perfect fit.

 

you did realize i was being sarcastic about the 1.5" reducer right, i thought i layed the sarcasm on there thick enough to make it obvious.

anyway yeah basically what you want is exhaust VELOCITY. dont worry about backpressure just build a system up that will move the gas out as fast as possible for your setup. best way to do this is with no obstructions/drastic changes in diameter or if there are any to make them as smoth as possible. also to size match the tubing size to the amount of air flow. the bigger the engine or the higher the rpm range the bigger the pipe.

team-integra.net has a good write up on exhaust theory too